Impedance-Based Adjustment of Power and Frequency

ABSTRACT

Systems and methods for impedance-based adjustment of power and frequency are described. A system includes a plasma chamber for containing plasma. The plasma chamber includes an electrode. The system includes a driver and amplifier coupled to the plasma chamber for providing a radio frequency (RF) signal to the electrode. The driver and amplifier is coupled to the plasma chamber via a transmission line. The system further includes a selector coupled to the driver and amplifier, a first auto frequency control (AFC) coupled to the selector, and a second AFC coupled to the selector. The selector is configured to select the first AFC or the second AFC based on values of current and voltage sensed on the transmission line.

CLAIM OF PRIORITY

The present patent application claims the benefit of and priority, under35 U.S.C. §119(e), to U.S. Provisional Patent Application No.61/701,560, filed on Sep. 14, 2012, and titled “Impedance-basedAdjustment of Power and Frequency”, which is incorporated by referenceherein in its entirety for all purposes.

The present patent application is a continuation-in-part of and claimsthe benefit of and priority, under 35 U.S.C. §120, to U.S. patentapplication Ser. No. 13/531,491, filed on Jun. 22, 2012, and titled“Methods and Apparatus For Controlling Plasma In A Plasma ProcessingSystem”, which is incorporated by reference herein in its entirety forall purposes.

The U.S. patent application Ser. No. 13/531,491 claims the benefit ofand priority, under 35 U.S.C. §119(e), to U.S. Provisional PatentApplication No. 61/602,040, filed on Feb. 22, 2012, and titled“Frequency Enhanced Impedance Dependent Power Control ForMulti-frequency Pulsing”, which is incorporated by reference herein inits entirety for all purposes.

The U.S. patent application Ser. No. 13/531,491 claims the benefit ofand priority, under 35 U.S.C. §119(e), to U.S. Provisional PatentApplication No. 61/602,401, filed on Feb. 23, 2012, which isincorporated by reference herein in its entirety for all purposes.

The present patent application is a continuation-in-part of and claimsthe benefit of and priority, under 35 U.S.C. §120, to U.S. patentapplication Ser. No. 13/550,719, filed on Jul. 17, 2012, and titled“Methods and Apparatus For Synchronizing RF Pulses In A PlasmaProcessing System”, which is incorporated by reference herein in itsentirety for all purposes.

The U.S. patent application Ser. No. 13/550,719 claims the benefit ofand priority, under 35 U.S.C. §119(e), to U.S. Provisional PatentApplication No. 61/602,041, filed on Feb. 22, 2012, and titled“Frequency Enhanced Impedance Dependent Power Control ForMulti-frequency Pulsing”, which is incorporated by reference herein inits entirety for all purposes.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is related to application Ser. No.13/620,386, filed on Sep. 14, 2012, titled “State-Based Adjustment ofPower and Frequency”, which is incorporated by reference herein in itsentirety for all purposes.

FIELD

The present embodiments relate to improving response time to a change inplasma impedance and/or to improving accuracy in stabilizing plasma, andmore particularly, to apparatus, methods, and computer programs forimpedance-based adjustment of power and frequency.

BACKGROUND

In some plasma processing systems, multiple radio frequency (RF) signalsare provided to one or more electrodes within a plasma chamber. The RFsignals help generate plasma within the plasma chamber. The plasma isused for a variety of operations, e.g., clean substrate placed on alower electrode, etch the substrate, etc.

Between a driver and amplifier system that generates a radio frequency(RF) signal and the plasma chamber, an impedance matching circuit isusually placed. The impedance matching circuit matches an impedance of aload, e.g., plasma within the plasma chamber, with an impedance of asource, e.g., the driver and amplifier system that generates the RFsignal. However, in certain situations, the impedance matching is notquick enough to respond to a change in the plasma impedance.

Moreover, although some systems are quick enough to respond to thechange, these systems may not result in accurate adjustment of powerand/or frequency to stabilize the plasma.

It is in this context that embodiments described in the presentdisclosure arise.

SUMMARY

Embodiments of the disclosure provide apparatus, methods and computerprograms for state-based adjustment of power and frequency. It should beappreciated that the present embodiments can be implemented in numerousways, e.g., a process, an apparatus, a system, a device, or a method ona computer-readable medium. Several embodiments are described below.

In an embodiment, a system includes a plasma chamber for containingplasma. The plasma chamber includes an electrode. The system includes adriver and amplifier (DA) system that is coupled to the plasma chamberfor providing a radio frequency (RF) signal to the electrode. The DAsystem is coupled to the plasma chamber via a transmission line. Thesystem further includes a selector coupled to the DA system, a firstauto frequency control (AFC) coupled to the selector, and a second AFCcoupled to the selector. The selector is configured to select the firstAFC or the second AFC based on values of current and voltage sensed onthe transmission line.

In one embodiment, a system includes a primary generator coupled to anelectrode. The primary generator includes a primary driver and amplifierfor supplying a primary radio frequency (RF) signal to the electrode.The primary generator further includes a primary automatic frequencytuner (AFT) to provide a first primary frequency input to the primarydriver and amplifier when a pulsed signal is in a first state. Theprimary AFT is configured to provide a second primary frequency input tothe primary driver and amplifier when the pulsed signal is in a secondstate. The system further includes a secondary generator coupled to theelectrode.

In this embodiment, the secondary generator includes a secondary driverand amplifier for supplying a secondary RF signal to the electrode. Thesecondary generator further includes a first secondary AFT coupled tothe secondary driver and amplifier. The secondary generator includes asecond secondary AFT coupled to the secondary driver and amplifier. Thesecondary generator also includes a processor, which is coupled to thefirst secondary AFT and the second secondary AFT. The secondarygenerator further includes a sensor coupled to the electrode. The sensoris used for sensing current and voltage transferred between thesecondary generator and the electrode during the first and secondstates. The processor is configured to generate parameters based on thecurrent and voltage and is configured to determine whether a first oneof the parameters for the first state exceeds a first boundary andwhether a second one of the parameters for the second state exceeds asecond boundary. The first secondary AFT is configured to provide afirst secondary frequency input to the secondary driver and amplifierupon receiving the determination that the first parameter exceeds thefirst boundary and the second secondary AFT configured to provide asecond secondary frequency input to the secondary driver and amplifierupon receiving the determination that the second parameter exceeds thesecond boundary.

In an embodiment, a system including a digital pulsing source forgenerating a pulsed signal is described. The system includes a primarygenerator. The primary generator includes a primary driver and amplifiercoupled to an electrode for supplying a primary radio frequency (RF)signal to the electrode. The primary generator also includes one or moreprimary processors coupled to the pulsing source for receiving thepulsed signal. The one or more primary processors are configured toidentify a first one of two states of the pulsed signal and a second oneof the two states, determine to provide a primary power value to theprimary driver and amplifier when the pulsed signal is in the firststate, and determine to provide a primary frequency value of the primaryRF signal when the pulsed signal is in the first state.

In this embodiment, the system further includes a secondary generator,which includes a secondary driver and amplifier coupled to the electrodefor supplying a secondary RF signal to the electrode. The secondarygenerator further includes one or more secondary processors coupled tothe pulsing source for receiving the pulsed signal. The one or moresecondary processors are configured to determine whether a parameterassociated with plasma exceeds a first boundary when the pulsed signalis in the first state, determine whether the parameter exceeds a secondboundary when the pulsed signal is in the second state, and determine toprovide a first secondary power value to the secondary driver andamplifier in response to determining that the parameter exceeds thefirst boundary. The one or more secondary processors are furtherconfigured to determine to provide a second secondary power value to thesecondary driver and amplifier in response to determining that theparameter exceeds the second boundary, determine to provide a firstsecondary frequency value to the secondary driver and amplifier inresponse to determining that the parameter exceeds the first boundary,and determine to provide a second secondary frequency value to thesecondary driver and amplifier in response to determining that theparameter exceeds the second boundary.

In an embodiment, a method includes receiving a digital pulsing signal,which has two states. The method includes receiving current and voltagevalues, calculating parameters associated with plasma impedance from thecurrent and voltage power values, and determining during the first statewhether a first one of the parameters exceeds a first boundary. Themethod also includes providing a first frequency value and a first powervalue to a radio frequency (RF) driver and amplifier upon determiningthat the first parameter exceeds the first boundary, determining duringthe second state whether a second one of the parameters exceeds a secondboundary, and providing a second frequency value and a second powervalue to the RF driver and amplifier upon determining that the secondparameter exceeds the second boundary.

Some advantages of the above-described embodiments include providing anaccurate power and/or frequency value to stabilize plasma, e.g., toreduce a difference between an impedance of a source, e.g., RF driverand amplifier, and a load, e.g., plasma. The frequency and/or powervalue is accurate when the power and/or frequency value is generatedbased on a change in plasma impedance. For example, forward power andreflected power are measured and are used to generate a gamma value. Itis determined whether the gamma value exceeds a threshold and if so, thepower and/or frequency value is changed to stabilize plasma.

Other advantages of embodiments include reducing an amount of time toachieve stability in plasma. A training routine is used to determinefrequency and/or power values to apply to a driver and amplifier system.The power and/or frequency values correspond to a gamma value that isalso determined during the training routine. The training routine savestime during production, e.g., time for cleaning substrates, time foretching substrates, time for deposition material on substrates, etc. Forexample, during production, when it is determined that the gamma valueexceeds a threshold, the power and/or frequency values are applied tothe driver and amplifier system without a need to tune the power and/orfrequency values.

Other aspects will become apparent from the following detaileddescription, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of a system for changing astate based on plasma impedance, in accordance with an embodimentdescribed in the present disclosure.

FIG. 2 is an embodiment of a table showing a change in states based onwhether a gamma value is greater than a first threshold or a secondthreshold, in accordance with an embodiment described in the presentdisclosure.

FIG. 3 shows an embodiment of a graph, which is a plot of a forwardpower versus time of two RF signals during a training routine, inaccordance with an embodiment described in the present disclosure.

FIG. 4 is an embodiment of a flowchart of a training routine, inaccordance with an embodiment described in the present disclosure.

FIG. 5 is a diagram of an embodiment of a system for changing a statebased on plasma impedance, where the power controllers and/or thefrequency tuners do not provide non-zero values, in accordance with anembodiment described in the present disclosure.

FIG. 6A shows graphs with two radio frequency (RF) signals in which oneof the RF signals has a constant value or varying values, in accordancewith an embodiment described in the present disclosure.

FIG. 6B shows graphs with two RF signals in which both the RF signalshave varying values, in accordance with an embodiment described in thepresent disclosure.

FIG. 7A shows graphs with three RF signals in which one of the RFsignals has a constant value and another one of the RF signals has aconstant value or varying values, in accordance with an embodimentdescribed in the present disclosure.

FIG. 7B shows graphs with three RF signals in which one of the RFsignals a constant value and the remaining two RF signals have varyingvalues, in accordance with an embodiment described in the presentdisclosure.

FIG. 7C shows graphs with three RF signals in which one of the RFsignals has a constant value or varying values and the remaining two RFsignals have varying values, in accordance with an embodiment describedin the present disclosure.

FIG. 7D shows graphs with all three RF signals have varying values, inaccordance with an embodiment described in the present disclosure.

FIG. 7E shows graphs with three RF signals in which one of the RFsignals has a constant value or varying values and the remaining RFsignals have varying values, in accordance with an embodiment describedin the present disclosure.

FIG. 7F shows graphs with all three RF signals have varying values, inaccordance with an embodiment described in the present disclosure.

FIG. 8 is a block diagram of an embodiment of a system for selectingbetween auto frequency tuners (AFTs) based on whether a gamma value isgreater than a first threshold or a second threshold, in accordance withan embodiment described in the present disclosure.

FIG. 9 is a flowchart of an embodiment of a method for adjusting afrequency and/or power of a 60 MHz driver and amplifier to achieve astate S1 or S0 of a 60 MHz generator, in accordance with an embodimentdescribed in the present disclosure.

FIG. 10 shows an embodiment of a graph of normalized RF variables versustime for implementing RF tuning by a dependent RF generator for optimalproduction time power delivery during independent (IP) RF signalpulsing, in accordance with one embodiment described in the presentdisclosure.

FIG. 11 is an embodiment of a flowchart of a method for implementingfrequency tuning by a dependent RF generator for optimal power deliveryduring pulsing, in accordance with an embodiment described in thepresent disclosure.

DETAILED DESCRIPTION

The following embodiments describe systems and methods forimpedance-based adjustment of power and frequency. It will be apparentthat the present embodiments may be practiced without some or all ofthese specific details. In other instances, well known processoperations have not been described in detail in order not tounnecessarily obscure the present embodiments.

FIG. 1 is a block diagram of an embodiment of a system 180 for changinga state based on plasma impedance. A 2 megahertz (MHz) radio frequency(RF) driver and amplifier (DA) system supplies RF power via an impedancematching circuit 182 to a lower electrode 104 of a plasma chamber 102.Similarly, a 60 MHz DA system supplies RF power via an impedancematching circuit 186 to the lower electrode 104. It should be noted thatin one embodiment, instead of the 60 MHz source, a 27 MHz source is usedto provide RF power to the lower electrode 104. Moreover, it should benoted that the values 2 MHz, 27 MHz, and 60 MHz are provided as examplesand are not limiting. For example, instead of the 2 MHz DA system, a 2.5MHz DA system may be used and instead of the 60 MHz DA system, a 65 MHzDA system may be used. In another embodiment, in addition to the 2 MHzsource and the 60 MHz sources, the 27 MHz source is used to provide RFpower to the lower electrode 104.

An impedance matching circuit includes electric circuit components,e.g., inductors, capacitors, etc. to match an impedance of a powersource coupled to the impedance matching circuit with an impedance of aload coupled to the impedance matching circuit. For example, theimpedance matching circuit 182 matches an impedance of the 2 MHz DAsystem with an impedance of plasma generated within the plasma chamber102. As another example, an impedance matching circuit 186 matches animpedance of the 60 MHz DA system with an impedance of plasma generatedwithin the plasma chamber 102. As yet another example, the impedancematching circuit 182 matches an impedance of the 2 MHz DA system with animpedance of a portion, e.g., the plasma and the lower electrode 104, ofthe plasma chamber 102. In one embodiment, an impedance matching circuitis tuned to facilitate a match between an impedance of an RF DA systemcoupled to the impedance matching circuit and an impedance of a load. Animpedance match between a power source and a load reduces chances ofpower being reflected from the load towards the power source.

The plasma chamber 102 includes the lower electrode 104, an upperelectrode 110, and other components (not shown), e.g., an upperdielectric ring surrounding the upper electrode 110, a lower electrodeextension surrounding the upper dielectric ring, a lower dielectric ringsurrounding the lower electrode, a lower electrode extension surroundingthe lower dielectric ring, an upper plasma exclusion zone (PEZ) ring, alower PEZ ring, etc. The upper electrode 110 is located opposite to andfacing the lower electrode 104. A substrate 108, e.g., a semiconductorwafer, is supported on an upper surface 106 of the lower electrode 104.Integrated circuits, e.g., application specific integrated circuit(ASIC), programmable logic device (PLD), etc. are developed on thesubstrate 108 and the integrated circuits are used in a variety ofdevices, e.g., cell phones, tablets, smart phones, computers, laptops,networking equipment, etc. The lower electrode 104 is made of a metal,e.g., anodized aluminum, alloy of aluminum, etc. Also, the upperelectrode 110 is made of a metal, e.g., aluminum, alloy of aluminum,etc.

In one embodiment, the upper electrode 110 includes a hole that iscoupled to a central gas feed (not shown). The central gas feed receivesone or more process gases from a gas supply (not shown). Examples of aprocess gases include an oxygen-containing gas, such as O₂. Otherexamples of a process gas include a fluorine-containing gas, e.g.,tetrafluoromethane (CF₄), sulfur hexafluoride (SF₆), hexafluoroethane(C₂F₆), etc. The upper electrode 110 is grounded. The lower electrode104 is coupled to the 2 MHz RF DA system via the impedance matchingcircuit 182 and to the 60 MHz RF DA system via the impedance matchingcircuit 186.

When the process gas is supplied between the upper electrode 110 and thelower electrode 104 and when a DA system, e.g., the 2 MHz DA systemand/or the 60 MHz DA system, supplies power via a correspondingimpedance matching circuit to the lower electrode 104, the process gasis ignited to generate plasma within the plasma chamber 102. Forexample, the 2 MHz DA system supplies power via the impedance matchingcircuit 182 to ignite the process gas to generate plasma.

A tool user interface (UI) 190 on a computer (not shown) is used togenerate a transistor-transistor logic (TTL) signal 112, which is adigital pulsing signal. In one embodiment, the computer includes a TTLcircuit. As used herein, instead of a computer, a processor, acontroller, an ASIC, or a PLD is used, and these terms are usedinterchangeably herein. The TTL signal 112 includes states S1 and S0.The TTL signal 112 has a 50% duty cycle. In one embodiment, the TTLsignal 112 has a duty cycle ranging from 5% to 95%. An example of thestate S1 includes an on state, a state having a value of 1, or a highstate. An example of the state S0 includes an off state, a state havinga value of 0, or a low state. The high value is greater than the lowvalue.

In another embodiment, instead of the computer, a clock oscillator,e.g., a crystal oscillator, is used to generate an analog clock signal,which is converted by an analog-to-digital converter into a digitalsignal similar to the TTL signal 112. For example, a crystal oscillatoris made to oscillate in an electric field by applying a voltage to anelectrode near or on the crystal oscillator.

The TTL signal 112 is sent to a digital signal processor (DSP) 140 andanother DSP 150. The DSP 140 receives the TTL signal 112 and identifiesthe states S0 and S1 of the TTL signal 112. For example, the DSP 140distinguishes between the states S0 and S1. As another example, the DSP140 determines that the TTL signal 112 has a first magnitude during afirst set of time periods and has a second magnitude during a second setof time periods. The DSP 140 determines that the TTL signal 112 has thestate S1 during the first set of time periods and has the state S0during the second set of time periods. As yet another example, the DSP140 compares a magnitude of the TTL signal 112 with a pre-stored valueto determine that the magnitude of the TTL signal 112 is greater thanthe pre-stored value during the first set of time periods and that themagnitude during the state S0 of the TTL signal 112 is not greater thanthe pre-stored value during the second set of time periods. In theembodiment in which the clock oscillator is used, the DSP 140 receivesan analog clock signal from the clock oscillator, converts the analogsignal into a digital form, and then identifies the two states S0 andS1.

The DSP 140 stores the identified states S0 and S1 in memory locationsof one or more memory devices within the DSP. Examples of a memberdevice include a random access memory (RAM) and a read-only memory(ROM). A memory device may be a flash memory, a hard disk, a storagedevice, a computer-readable medium, etc.

The DSP 140 provides the identified state S1 from corresponding memorylocations to an auto frequency tuner (AFT) 114 and to a power controller142. For example, the DSP 140 indicates to the AFT 114 and the powercontroller 142 that the TTL signal 112 is in the state S1 between timest1 and t2 of a duty cycle. The terms tuner and controller are usedinterchangeably herein. An example of an AFT is provided in U.S. Pat.No. 6,020,794, which is incorporated by reference herein in itsentirety.

In one embodiment, instead of a controller or a tuner, a control logicblock, e.g., a computer program, that is executed by a processor isused. For example, each AFT of a generator is a logic block that isexecuted by a processor of the generator. As another example, each powercontroller of a generator is a logic block that is executed by aprocessor of the generator. A computer program is embodied in anon-transitory computer-readable medium, examples of which are providedbelow.

The AFT 114 determines a frequency value based on a state of the TTLsignal 112 and the power controller 142 determines a power value basedon a state of the TTL signal 112. For example, the AFT 114 determinesthat a frequency value F11 is to be provided to the 2 MHz DA system whenthe state of the TTL signal 112 is S1 and the power controller 142determines that a power value P11 is to be provided to the 2 MHz DAsystem when the state of the TTL signal 112 is S1.

When the state of the TTL signal 112 is S1, the power controller 142provides the power value of P11 to the 2 MHz DA system. During the stateS1 of the TTL signal 112, the AFT 114 provides the frequency value ofF11 to the 2 MHz DA system.

The 2 MHz DA system receives the frequency value of F11 and the powervalue of P11 during the state S1. Upon receiving the values F11 and P11,the 2 MHz DA system generates an RF signal having the frequency F11 andthe RF signal has the power value of P11.

In one embodiment, an RF DA system includes a driver followed by anamplifier. The amplifier supplies forward power via a transmission lineto the plasma chamber 102. For example, the amplifier of the 2 MHz DAsystem supplies forward power having a power value that is proportional,e.g., same as, multiple of, etc. to the power value P11 and having thefrequency value F11 via a transmission line 230 and the impedancematching circuit 182 to the plasma chamber 102.

When the TTL signal 112 transitions from the state S1 to the state S1and when the 2 MHz DA system supplies forward power having the powervalue proportional to the power value P11 and having the frequency valueF11 to the plasma chamber 102, impedance with the plasma chamber 102changes. When the impedance within the plasma chamber 102 changes as aresult of transition of the TTL signal 112 from the state S1 to thestate S0, a sensor 212 of a 60 MHz generator 276 measures forward powerand reflected power, which is RF power reflected from the plasma of theplasma chamber 102, on a transmission line 232. The sensor 212 providesthe measurement of the forward and reflected powers to ananalog-to-digital (ADC) converter 222, which converts the measurementsfrom an analog format to a digital format. The digital values of theforward and reflected powers are provided to a DSP 150. In anembodiment, a DSP includes an ADC. It should further be noted that inone embodiment, the DSP 150 lacks reception of the TTL signal 112.Rather, in this embodiment, the DSP 150 receives another digital pulsedsignal that may not be synchronous with the TTL signal 112. In oneembodiment, the other digital pulsed signal received by the DSP 150 issynchronous with the TTL signal 112.

During the state S1 of the TTL signal 112, e.g., immediately after thestate transition from S1 to S0 of the TTL signal 112, the DSP 150calculates a relationship, e.g., a square root of a ratio of the digitalreflected power signal and the digital forward power signal, a voltagestanding wave ratio (VSWR), etc., during the state S1 to generate afirst gamma value. A gamma value of 1 indicates a high degree ofmismatch between impedances of a source and a load and a gamma value of0 indicates a low degree of mismatch between impedances of a source anda load. If a gamma value is zero, power delivery to the plasma chamber102 is deemed highly efficient. If the gamma value is 1, the powerdelivery is deemed highly inefficient. The VSWR is calculated as beingequal to a ratio of RC−1 and RC+1, where RC is a reflection coefficient.

The DSP 150 determines whether the first gamma value is greater than afirst threshold. When the DSP 150 determines that the first gamma valueis greater than the first threshold, the DSP 150 indicates the same toan AFT 118 and to a power controller 152. The AFT 118 determines afrequency value F21 corresponding to the first gamma value and providesthe frequency value F21 to the 60 MHz DA system. Moreover, the powercontroller 152 determines a power value P21 corresponding to the firstgamma value and provides the power value P21 corresponding to the firstgamma value to the 60 MHz DA system. For example, the AFT 118 storeswithin a memory device, a table that maps the first gamma value with thefrequency value F21 and the power controller 152 stores within a memorydevice a mapping between the power value P21 and the first gamma value.

In one embodiment, the AFT 118 determines each of the frequency valueF21 and the power value P21 as corresponding to the first threshold. Forexample, the AFT 118 stores within a memory device, a table that mapsthe first threshold with the frequency value F21 and the powercontroller 152 stores within a memory device a mapping between the powervalue P21 and the first threshold.

The 60 MHz DA system receives the frequency value of F21 and the powervalue of P21 during the state S1 of the TTL signal 112. Upon receivingthe values F21 and P21, the 60 MHz DA system generates an RF signalhaving the frequency F21 and the RF signal has the power value of P21.For example, an amplifier of the 60 MHz DA system supplies forward powerhaving a power value that is proportional, e.g., same as, multiple of,etc. to the power value P21 and having the frequency value F21 via thetransmission line 232 and the impedance matching circuit 186 to theplasma chamber 102.

When the state of the TTL signal 112 changes from S1 to S0, no powervalue and no frequency value is provided to the 2 MHz DA system. Duringthe state S0, no frequency value is provided to the 2 MHz DA system. The2 MHz DA system does not receive any frequency and power values, e.g.,receives the frequency value of 0 and the power value of 0, during thestate S0. Upon not receiving power and frequency values, the 2 MHz DAsystem generates RF power at a frequency of zero and RF power having apower value of zero. The amplifier of the 2 MHz DA system does notsupply forward power, e.g., supplies forward power having a power valueof zero and having a frequency value of zero, via the transmission line230 and the impedance matching circuit 182 to the plasma chamber 102.

Moreover, when the state of the TTL signal 112 changes to the state S0from the state S1, the impedance of plasma within the plasma chamber 102changes. Again, during the state S0 of the TTL signal 112, e.g.,immediately after the transition from the state S1 to the state S0 ofthe TTL signal 112, the sensor 212 determines the forward and reflectedpowers on the transmission line 232 and provides the measured forwardand reflected powers to an ADC 222. The ADC 222 converts the measuredforward and reflected powers from analog format to a digital format. TheDSP 150 receives the digital forward and reflected powers from the ADC222 and calculates a second gamma value from the forward and reflectedpowers.

The DSP 150 compares the second gamma value to a second threshold anddetermines whether the second gamma value is greater than the secondthreshold. When the DSP 150 determines that the second gamma value isgreater than the second threshold, the DSP 150 indicates the same to anAFT 118 and to the power controller 152. The AFT 118 determines afrequency value F20 corresponding to the second gamma value and providesthe frequency value F20 to the 60 MHz DA system. Moreover, the powercontroller 152 determines a power value P20 corresponding to the secondgamma value and provides the power value P20 corresponding to the secondgamma value to the 60 MHz DA system. For example, the AFT 118 storeswithin a memory device, a table that maps the second gamma value withthe frequency value F20 and the power controller 152 stores within amemory device a mapping between the power value P20 and the second gammavalue.

In one embodiment, the AFT 118 determines each of the frequency valueF20 and the power value P20 as corresponding to the second threshold.For example, the AFT 118 stores within a memory device, a table thatmaps the second threshold with the frequency value F20 and the powercontroller 152 stores within a memory device a mapping between the powervalue P20 and the second threshold.

The 60 MHz DA system receives the frequency value of F20 and the powervalue of P20 during the state S0 of the TTL signal 112. Upon receivingthe values F20 and P20, the 60 MHz DA system generates an RF signalhaving the frequency F20 and the RF signal has the power value of P20.For example, an amplifier of the 60 MHz DA system supplies forward powerhaving a power value that is proportional, e.g., same as, multiple of,etc. to the power value P20 and having the frequency value F20 via thetransmission line 232 and the impedance matching circuit 186 to theplasma chamber 102.

The use of measurement of forward and reflected powers to change RFpower provided by the 60 MHz DA system results in plasma stability.Also, the plasma stability is based on real-time measurement of forwardand reflected powers. This real-time measurement provides accuracy instabilizing the plasma.

In one embodiment, during one or both the states S1 and S0, a sensor 210of the 2 MHz generator 274 senses RF power reflected from the plasma ofthe plasma chamber 102 on the transmission line 230. Moreover, duringone or both the states S1 and S0, the sensor 210 senses forward power onthe transmission line 230 when the forward power is sent from the 2 MHzRF DA system via the transmission line 230 to the plasma chamber 102.Similarly, during one or both the states S1 and S0, the sensor 212senses power reflected from the plasma of the plasma chamber 102. Thereflected power sensed by the sensor 212 is reflected on thetransmission line 232 from the plasma of the plasma chamber 102.Moreover, during one or both the states S1 and S0 of the TTL signal 112,the sensor 212 senses forward power on the transmission line 232 whenthe forward power is sent from the 60 MHz RF DA system via thetransmission line 232 to the plasma chamber 102.

In this embodiment, an analog-to-digital converter (ADC) 220 convertsthe measured reflected and forward powers sensed by the sensor 210 froman analog form to a digital form and the ADC 222 converts the measuredreflected and forward powers sensed by the sensor 212 from an analog toa digital form. During one or both the states S1 and S0, the DSP 140receives the digital values of the reflected power signal and theforward power signal sensed by the sensor 210 and the DSP 150 receivesthe digital value of the reflected power signal and the forward powersignal sensed by the sensor 212.

Furthermore, in this embodiment, a gamma value that is generated fromthe digital values of the forward and reflected powers on thetransmission line 230 during the state S1 is sent from the DSP 140 tothe AFT 114 and a gamma value that is generated from the digital valuesof the forward and reflected powers on the transmission line 232 duringthe state S1 is sent from the DSP 150 to the AFT 118. During the stateS1, the AFT 114 determines a frequency value based on the value of gammareceived from the DSP 140 and the AFT 118 determines a frequency valuebased on the value of gamma received from the DSP 150. During the stateS1, the AFT 114 adjusts the frequency value of F11 based on thefrequency value that is generated based on the gamma value and providesthe adjusted frequency value to the 2 MHz DA system. Moreover, duringthe state S1, the AFT 118 adjusts the frequency value of F21 based onthe frequency value that is generated based on the gamma value andprovides the adjusted frequency value to the 60 MHz DA system.

Moreover, in the same embodiment, during the state S1, the powercontroller 142 determines a power value based on the value of gammareceived from the DSP 140 and the power controller 152 determines apower value based on the value of gamma received from the DSP 150.During the state S1, the power controller 142 adjusts the power value ofP11 based on the power value that is generated based on the gamma valueand provides the adjusted power value to the 2 MHz DA system. Moreover,during the state S1, the power controller 152 adjusts the power value ofP21 based on the power value that is generated based on the gamma valueand provides the adjusted power value to the 60 MHz DA system.

Further, in this embodiment, during the state S1, the 2 MHz DA systemgenerates a power signal having the adjusted frequency value receivedfrom the AFT 114 and having the adjusted power value received from thepower controller 142, and supplies the power signal via the impedancematching circuit 182 to the plasma chamber 102. Similarly, during thestate S1, the 60 MHz DA system generates a power signal having theadjusted frequency value received from the AFT 118 and having theadjusted power value received from the power controller 152, andsupplies the power signal via the impedance matching circuit 186 to theplasma chamber 102.

Furthermore, in the same embodiment, during the state S0, there is noprovision of power and frequency values to the 2 MHz DA system and thereis no use of a gamma value generated during the state S0 to adjust thezero frequency and power values of the 2 MHz DA system. A gamma valuethat is generated from the digital values of the forward and reflectedpowers on the transmission line 232 during the state S0 is sent from theDSP 150 to the AFT 120. The AFT 120 determines a frequency value basedon the value of gamma received from the DSP 150. During the state S0,the AFT 120 adjusts the frequency value of F20 based on the frequencyvalue that is generated from the gamma value and provides the adjustedfrequency value to the 60 MHz DA system. Moreover, during the state S0,the power controller 154 determines a power value based on the value ofgamma received from the DSP 150. During the state S0, the powercontroller 154 adjusts the power value of P20 based on the power valuethat is generated based on the gamma value and provides the adjustedpower value to the 60 MHz DA system. During the state S0, the 60 MHz DAsystem generates a power signal having the adjusted frequency valuereceived from the AFT 120 and having the adjusted power value receivedfrom the power controller 154, and supplies the power signal via theimpedance matching circuit 186 to the plasma chamber 102.

It should be noted that in this embodiment, a difference between anadjusted value that is generated by adjusting a value and the value issmaller than a difference between another power or frequency value thatis generated by using the first or second threshold. For example, adifference between the adjusted power value generated from the powervalue P21 and the power value P21 is less than a difference between thepower values P21 and P20. As another example, a difference between theadjust frequency value generated from the frequency value F20 and thefrequency value F20 is less than a difference between the frequencyvalues F21 and F20.

The power controller 142, the AFT 114, and the DSP 140 are parts of agenerator controller 270. The generator controller 270, the ADC 220, thesensor 210, and the 2 MHz DA system are parts of a 2 MHz generator 274.Similarly, the power controller 152, the power controller 154, the AFTs118 and 120, and the DSP 150 are parts of a generator controller 272.The generator controller 272, the ADC 222, the sensor 212, and the 60MHz DA system are parts of the 60 MHz generator 276.

In one embodiment, the system 180 excludes the impedance matchingcircuits 182 and/or 186. In an embodiment, a single controller is usedinstead of the power controller 142 and the AFT 114, a single controlleris used instead of the power controller 152 and the AFT 118, and asingle controller is used instead of the power controller 154 and theAFT 120.

In the embodiment in which the 27 MHz DA system is used in addition tousing the 2 and 60 MHz power supplies, a 27 MHz generator is similar tothe 60 MHz generator 276 except that the 27 MHz generator includes the27 MHz DA system instead of the 60 MHz DA system. The 27 MHz generatoris coupled to the lower electrode 104 of the plasma chamber 102 via animpedance matching circuit (not shown) and a transmission line (notshown). Moreover, the 27 MHz DA system is coupled to a digital pulsedsignal source, other than the Tool UI 112, and a digital pulsed signalgenerated by the digital pulsed signal source may not be synchronouswith the TTL signal 112. An example of a digital pulsed signal sourceincludes a clock oscillator or a computer that includes a TTL circuitthat generates a TTL signal. In one embodiment, the digital pulsedsignal generated by the digital pulsed signal source is synchronous withthe TTL signal 112. The 27 MHz generator includes two power controllers,two AFTs, a DSP, an ADC, a sensor, and the 27 MHz DA system.

In an embodiment, the first threshold and the second threshold aregenerated during a training routine, e.g., a learning process. Duringthe training routine, when the 2 MHz DA system changes its RF powersignal from a low power value to a high power value, there is animpedance mismatch between one or more portions, e.g., plasma, etc.,within the plasma chamber 102 and 60 MHz DA system. The high power valueis higher than the low power value. The 2 MHz DA system changes a stateof its RF power signal from the low power value to the high power valuewhen a state of the TTL signal 112 or a clock signal supplied to the 2MHz RF DA system changes from S0 to S1. In this case, the 60 MHz DAsystem has its frequency and power tuned when the 2 MHz DA system startssupplying power at the high power value. To reduce the impedancemismatch, the 60 MHz DA system starts tuning, e.g., converging, to apower value and to a frequency value. The convergence may be determinedby the DSP 150 based on a standard deviation or another technique. Toallow the 60 MHz DA system more time to converge to the power value andto the frequency value, the 2 MHz DA system is kept at the high powervalue for an extended period of time than a usual period of time. Theusual period of time is an amount of time in which the impedancemismatch is not reduced, e.g., removed. An example of the usual periodof time is equal to half cycle of the TTL signal 112. When the 60 MHz DAsystem converges to the power value and the frequency value, theconverged power value is stored as the power value P21 within the powercontroller 152 and the converged frequency value is stored as thefrequency value F21 within the AFT 118. The first threshold is generatedfrom the power value P21 during the training routine and the first gammavalue corresponds to the frequency value F21. For example, the sensor212 measures the forward power value and a reflected power value duringthe training routine. The sensor 212 measures the forward and reflectedpower values during the training routine when the frequency of the 60MHz signal is F21. The ADC 222 converts the measured forward andreflected values from an analog format to a digital format. The DSP 150receives the digital forward power value of P21 and the digitalreflected power value from the ADC 222 and generates the first thresholdfrom the power value P21 and the digital reflected power value measuredduring the training routine.

Similarly, during the training routine, the power value P20 and thefrequency values F20 are generated when the 2 MHz DA system changes itsRF power signal from the high power value to the low power value. Thepower value P20 is stored in the power controller 154 and the frequencyvalue F20 is stored in the AFT 120. Also, the power value P20 is used togenerate the second threshold during the training routine in a similarmanner in which the first threshold is generated from the power valueP21. The second threshold corresponds to the frequency value F20. Forexample, when the power value of the 60 MHz signal is determined to beP20, the frequency value of the 60 MHz signal is F20.

In an embodiment, instead of the DSP 150, the AFT 118 and the powercontroller 152 determine whether the first gamma value is greater thanthe first threshold. In this embodiment, the DSP 150 provides the firstgamma value to the AFT 118 and the power controller 152. When the AFT118 determines that the first gamma value is greater than the firstthreshold, the AFT 118 determines the frequency value F21 correspondingto the first gamma value and provides the frequency value F21 to the 60MHz DA system. Moreover, when the power controller 152 determines thatthe first gamma value is greater than the first threshold, the powercontroller 152 determines the power value P21 corresponding to the firstgamma value and provides the power value P21 to the 60 MHz DA system.

Moreover, in this embodiment, instead of the DSP 150, the AFT 120 andthe power controller 154 determine whether the second gamma value isgreater than the second threshold. In this embodiment, the DSP 150provides the second gamma value to the AFT 120 and the power controller154. When the AFT 120 determines that the second gamma value is greaterthan the second threshold, the AFT 120 determines the frequency valueF20 corresponding to the second gamma value and provides the frequencyvalue F20 to the 60 MHz DA system. Moreover, when the power controller154 determines that the second gamma value is greater than the secondthreshold, the power controller 154 determines the power value P20corresponding to the second gamma value and provides the power value P20to the 60 MHz DA system.

In an embodiment, instead of the sensor 212 sensing the forward andreflected powers, complex voltage and current are sensed and gamma isgenerated from the sensed values voltage and current. For example, oneor more sensors, e.g., voltage sensors, current sensors, etc. sensecurrent and voltage on the transmission line 232, and provide the sensedcurrent and voltage values as complex values to the DSP 150. The DSP 150calculates forward and reflected powers from the sensed current andvoltage values, and generates gamma values from the forward andreflected powers.

In one embodiment, instead of the sensor 212 sensing the forward andreflected powers, during the state S1 of the TTL signal 106, a firstcomparator compares voltage or current, which is reflected on thetransmission line 232, to determine whether the voltage or current isgreater than a first pre-determined value. During the state S1 of theTTL signal 106, when the voltage or current is greater than the firstpre-determined value, the first comparator provides a first signal tothe DSP 150 and when the voltage or current is not greater than thefirst pre-determined value, the comparator provides a second signal tothe DSP 150. In response to receiving the first signal, the DSP 150identifies that the voltage or current is greater than the firstpre-determined value and in response to receiving the second signal, theDSP 150 identifies that the voltage or current does not exceed the firstpre-determined value. When the DSP 150 identifies that the voltage orcurrent exceeds the first pre-determined value, the DSP 150 determinesthe frequency value F21 corresponding to the first pre-determined valueand provides the frequency value F21 to the AFT 118. Moreover, uponreceiving the indication that the voltage or current exceeds the firstpre-determined value, the DSP 150 determines the power value P21corresponding to the first pre-determined value and provides the powervalue P21 to the power controller 152. The comparator is coupled to theDSP 150.

In this embodiment, during the state S0 of the TTL signal 106, thecomparator compares voltage or current, which is reflected on thetransmission line 232, to determine whether the voltage or current isgreater than a second pre-determined value. When the voltage or currentis greater than the second pre-determined value, the comparator providesthe first signal to the DSP 150 and when the voltage or current is notgreater than the second pre-determined value, the comparator providesthe second signal to the DSP 150. In response to receiving the firstsignal during the state S0 of the TTL signal 106, the DSP 150 identifiesthat the voltage or current is greater than the second pre-determinedvalue and in response to receiving the second signal during the state S0of the TTL signal 106, the DSP 150 identifies that the voltage orcurrent does not exceed the second pre-determined value. When the DSP150 determines that the voltage or current exceeds the secondpre-determined value, the DSP 150 determines the frequency value F20corresponding to the second pre-determined value and provides thefrequency value F20 to the AFT 120. Moreover, upon receiving theindication that the voltage or current exceeds the second pre-determinedvalue, DSP 150 determines the power value P20 corresponding to thesecond pre-determined value and provides the power value P20 to thepower controller 154. In an embodiment, a comparator includes analogcircuitry, e.g., one or more operational amplifiers.

FIG. 2 is an embodiment of a table 250 showing a change in states basedon whether a gamma value is greater than the first threshold or thesecond threshold. As indicated in the table 250, the TTL signal 112 isused to provide a digital pulsed signal, e.g., a clock signal, to theDSP 140 (FIG. 1).

When the TTL signal 112 is in the state S1, the 2 MHz signal has thehigh power level. During the state S1 of the TTL signal 112, it isdetermined whether a gamma value exceeds the first threshold. Inresponse to determining that the gamma value exceeds the firstthreshold, power value of the 60 MHz signal is changed to the powervalue P20 from the power value P21 and the frequency value of the 60 MHzsignal is changed from the frequency value F20 to the frequency valueF21 to achieve a state S1.

Also, when the TTL signal 112 is in the state S0, the 2 MHz signal hasthe low power level. During the state S0 of the TTL signal 112, it isdetermined whether a gamma value exceeds the second threshold. Inresponse to determining that the gamma value exceeds the secondthreshold, power value of the 60 MHz signal is changed to the powervalue P21 from the power value P20 and the frequency value of the 60 MHzsignal is changed from the frequency value F21 to the frequency valueF20 to achieve a state S0.

FIG. 3 shows an embodiment of a graph 111, which is a plot of a forwardpower versus time of two RF signals, the 2 MHz signal and the 60 MHzsignal during the training routine. In an embodiment, the trainingroutine is performed once to determine tuned RF values, e.g., the powervalues P20 and P21, the frequency values F20 and F21, the thresholdvalues, etc., or performed once during a time period to account for, forexample, plasma impedance. In this example, the 2 MHz signal is anindependently pulsing (IP) RF signal and the 60 MHz signal represents adependent RF signal that tunes its RF frequency to optimize powerdelivery when the 2 MHz RF signal pulses. Although only one dependent RFgenerator (e.g., 60 MHz) is discussed in connection with FIG. 3, itshould be understood that there may be multiple dependent RF generators,each of which may undergo a similar training routine to ascertain itsown optimal tuned RF frequencies and thresholds when the IP RF signalpulses.

FIG. 3 may be better understood when studied in conjunction with anembodiment of a flowchart of a method 113, which is described withreference to FIG. 4. The method 113 is an example of the trainingroutine.

At a point 115, an IP RF signal 119 of the IP RF generator (e.g., 2 MIIzgenerator) is pulsed high to a high power set point. In the example ofFIG. 1, the high power set point for the 2 MHz IP RF generator is 6kilowatts (kW). This is also shown in an operation 117 of FIG. 4.

Further, the dependent RF generator (e.g., 60 MHz generator) is set toits frequency self-tuning mode to allow the dependent RF generator toconverge to an optimal RF frequency for power delivery when the IP RFsignal 119 is pulsed high. This is also shown in the operation 117 ofFIG. 4. To elaborate, the independent or dependent RF generator monitorsmany variables associated with the plasma chamber 102 and adjusts itsown variables to maximize power delivery to the plasma chamber 102. Theindependent or dependent RF generator then tunes its RF signal frequencyto minimize gamma, thereby maximizing power delivery efficiency.

The IP RF signal of 2 MHz is pulsed high during the period betweenpoints 115 and 121. This high pulse duration of the IP RF signal isgreatly extended during the training time, e.g., from tenths of secondsup to multiple of seconds relative to an IP RF signal high pulseduration employed during production time for processing of the substrate108. The substrate 108 may be processed to etch the substrate 108, todeposit one or more layers on the substrate 108, to clean the substrate108, etc. This artificially extended high pulse duration gives thedependent RF generator enough time to optimally tune its frequency tomaximize power delivery efficiency for the plasma impedance conditionthat exists when the IP RF signal is pulsed high.

The dependent RF generator tunes to a frequency value of 61.3 MHz for agamma value of 0.04 when the 2 MHz IP RF signal pulses high. Thisoptimal tuned RF frequency of 61.3 MHz, e.g., IDPC_Freq1, for thedependent RF generator is then recorded within the AFT 118 (FIG. 1) asillustrated in operation 123 and is set as the IDPC_Freq1 as illustratedin an operation 125 of FIG. 4. The IDPC_Freq1 is an example of thefrequency value F21. Forward power, e.g., 6 kW, etc., sensed by thesensor 212 at the frequency IDPC_Freq1 is an example of the power valueP21. This 61.3 MHz value represents the optimal RF frequency for the 60MHz dependent RF signal when the 2 MHz IP RF signal pulses high. Thegamma value of 0.04 verifies that power delivery is efficient at thisoptimal tuned RF frequency for the dependent RF generator.

The dependent RF generator is then operated in the fixed frequency modewhereby its RF frequency is not allowed to tune. Instead, the dependentRF generator is forced to operate at the aforementioned 61.3 MHz optimaltuned RF frequency and the 2 MHz IP RF signal transitions from its highpower set point to its low power set point (from 121 to 127). This canbe seen in an operation 131 of FIG. 4. Although the low power set pointfor the 2 MHz RF signal is zero in the example of FIG. 2, in anembodiment, the low power set point may be any power level setting thatis lower than the high power set point of 6 kW.

After the IP RF signal pulses low (after point 127), the previousoptimal tuned RF frequency of 61.3 MHz is no longer efficient RFfrequency for power delivery by the dependent RF generator. This isbecause the plasma impedance has changed when the 2 MHz IP RF signalpulses low to deliver a lower amount of RF power to the plasma withinthe plasma chamber 102. The inefficiency is reflected in a gamma valueof 0.8, which is detected by the sensor 212 of the dependent RFgenerator. This gamma value of 0.8 is recorded in an operation 133 ofFIG. 4 and may be set as an IDPC_Gamma1 threshold in an operation 135 ofFIG. 4. The IDPC_Gamma1 threshold is an example of the second threshold.The IDPC_Gamma2 threshold is stored within a memory device of theDSP150, a memory device of the AFT 120, and/or a memory device of thepower controller 154 (FIG. 1).

During production time, as the IP RF signal is pulsed high and the 60MHz RF signal is at 61.3 MHz and the IDPC_Gamma1 threshold issubsequently encountered, the dependent RF generator determines that the2 MHz IP RF signal has just transitioned from high to low.

In one or more embodiments, the IDPC_Gamma1 threshold can be adjustedfor sensitivity by a Threshold 1 Adjust value. For example, it may bedesirable to set in the operation 135 the IDPC_Gamma1 threshold at 0.7instead of 0.8, e.g., slightly below a gamma value that exists due tothe high-to-low transition of the 2 MHz IP RF signal, to increase thehigh-to-low detection sensitivity by the sensor 212. In this example,the Threshold 1_Adjust value is −0.1, and the IDPC_Gamma 1 threshold of0.7 is the sum of the gamma value of 0.8 and the Threshold I Adjustvalue of −0.1.

Once the IDPC_Gamma1 threshold is obtained, the 60 MHz dependent RFgenerator is set to the frequency self-tuning mode in an operation 139to enable the 60 MHz dependent RF generator to determine an optimaltuned RF frequency for power delivery when the 2 MHz IP RF signal pulseslow. Again, the low pulse of the 2 MHz IP RF signal is artificiallyextended between points 127 and 137 of FIG. 3 to enable both anascertainment of the IDPC_Gamma 1 threshold and to permit the 60 MHzdependent RF generator to self-tune to an optimal RF frequency for powerdelivery during the low pulse of the 2 MHz IP RF signal.

Once the dependent RF generator tunes to the optimal RF frequency, e.g.,60.5 MHz, for power delivery during the low pulse of the 2 MHz IP RFsignal, the optimal tuned RF frequency of the dependent RF generator isrecorded in an operation 141 and is set as IDPC Freq 2 in an operation143.

After the dependent RF generator has tuned to its optimal RF frequencyvalue, e.g., 60.5 MHz, etc., for the low pulse of the 2 MHz IP RFsignal, the dependent RF generator is set to operate in a fixedfrequency mode in an operation 145 at an IDPC_Freq2 and the 2 MHz IP RFgenerator is allowed to pulse high, e.g., transition from the point 137to a point 147. The IDPC_Freq2 is an example of the frequency value F20.Forward power sensed by the sensor 212 at the frequency IDPC_Freq2 is anexample of the power value P20. This can also be seen in the operation145 of FIG. 4.

After the 2 MHz IP RF signal pulses high, e.g., after point 137, theprevious optimal tuned RF frequency IDPC_Freq2 is no longer theefficient RF frequency for power delivery by the 60 MHz RF generator.This is because the plasma impedance has changed when the 2 MHzindependently pulsing RF signal pulses high to deliver a higher amountof RF power to the plasma within the plasma chamber 102. Theinefficiency is reflected in a gamma value of 0.78, which is detected bythe sensor 212. This gamma value of 0.78 is recorded in an operation 151and may be set as an IDPC_Gamma2 threshold in an operation 153. THEIDPC_Gamma2 threshold is an example of the first threshold. TheIDPC_Gamma2 threshold is stored within a memory device of the DSP 150, amemory device of the AFT 118, and/or a memory device of the powercontroller 152.

During production time as the IP RF signal is pulsed low and the 60 MHzRF signal is at 60.5 MHz, which is the optimal tuned RF frequency forthe 60 MHz RF generator when the IP RF signal is pulsed low, and theIDPC_Gamma2 threshold is subsequently encountered, the dependent RFgenerator determines that the 2 MHz IP RF signal has just transitionedfrom low to high.

In one or more embodiments, the IDPC_Gamma2 threshold can be adjustedfor sensitivity by a Threshold2 Adjust value. For example, it may bedesirable to set at the operation 153 of FIG. 4 the IDPC_Gamma2threshold at 0.75 instead of 0.78, e.g., slightly below the true gammavalue that exists due to the low-to-high transition of the 2 MHz IP RFsignal, to increase the low-to-high detection sensitivity by the sensor212. In this example, the Threshold2_Adjust value is −0.03, and the IDPCGamma2 threshold of 0.75 is the sum of the gamma value of 0.78 and theThreshold2 Adjust value of −0.03.

The two optimal tuned RF frequencies values, e.g., 61.3 MHz and 60.5MHz, and the two gamma threshold values, e.g., IDPC_Gamma1 threshold andIDPC_Gamma2 threshold, are then employed during production time when the2 MHz is allowed to pulse and the 60 MHz dependent RF generator flipsback and forth between the two previously learned optimal tuned RFfrequencies when the sensor 212 detects that a gamma value has exceededthe thresholds. The 60 MHz signal is illustrated as a signal 155 in FIG.3.

FIG. 5 is a diagram of an embodiment of a system 262 for changing astate based on plasma impedance, where the power controllers and/or thefrequency tuners do not provide non-zero values. The system 262 issimilar to the system 180 of FIG. 1 except that the system 262 includesa power controller 172 and an AFT 264, each of which provide non-zerovalues.

The DSP 140 provides the identified state S0 from a corresponding memorylocation to the AFT 264 and to the power controller 172. As an example,the DSP 140 indicates to the AFT 264 and the power controller 172 thatthe TTL signal 112 is in the state S0 between times t2 and t3 of a dutycycle. The AFT 264 determines a frequency value based on a state of theTTL signal 112 and the power controller 172 determines a power valuebased on the state of the TTL signal 112. For example, the AFT 264determines that a frequency value F10 is to be provided to the 2 MHz DAsystem when the state of the TTL signal 112 is S0 and the powercontroller 172 determines that a power value P10 is to be provided tothe 2 MHz DA system when the state of the TTL signal 112 is S0. In oneembodiment, the values F10 and P10 are positive values.

The frequency value F10 is stored in the AFT 264 and the power value P10is stored in the power controller 172. When the state of the TTL signal112 is S0, the power controller 172 provides the power value of P10 tothe 2 MHz DA system and the AFT 264 provides the frequency value of F10to the 2 MHz DA system.

The 2 MHz DA system receives the frequency value of F10 and the powervalue of P10 during the state S0. Upon receiving the values F10 and P10,the 2 MHz DA system generates RF power at the frequency F10 and the RFpower has the power value of P10. The amplifier of the 2 MHz DA systemsupplies forward power having a power value that is proportional to thepower value P10 and having the frequency value F10 via the transmissionline 230 and the impedance matching circuit 182 to the plasma chamber102.

In an embodiment, during the state S0 of the TTL signal 112, the AFT 264determines a frequency value based on the value of gamma received fromthe DSP 140. During the state S0, the AFT 264 adjusts the frequencyvalue of F10 based on the frequency value that is generated from thegamma value and provides the adjusted frequency value to the 2 MHz DAsystem. Moreover, during the state S0, the power controller 172determines a power value based on the value of gamma received from theDSP 140. During the state S0, the power controller 172 adjusts the powervalue of P10 based on the power value that is generated based on thegamma value and provides the adjusted power value to the 2 MHz DAsystem. Also, during the state S0, the 2 MHz DA system generates a powersignal having the adjusted frequency value received from the AFT 264 andhaving the adjusted power value received from the power controller 172,and supplies the power signal via the impedance matching circuit 182 tothe plasma chamber 102.

The power controllers 142 and 172, the AFTs 114 and 264, and the DSP 140are parts of a generator controller 290. The generator controller 290,the ADC 220, the sensor 210, and the 2 MHz DA system are parts of a 2MHz generator 292.

In one embodiment, instead of each DSP 140 or 150, any number ofprocessors are used to perform the functions performed by the DSP.

FIG. 6A shows embodiments of graphs 302, 304, 306, and 308. Each graph302, 304, 306, and 308 plots power values in kilowatts (kW) as afunction of time t. As indicated in graph 302, a 2 MHz power signal,which is a power signal supplied by the 2 MHz DA system has a powervalue of a1 during the state S1 and has a power value of 0 during thestate S0. The power value a1 is an example of the power value P11. Also,a 60 MHz power signal, which is a power signal supplied by the 60 MHz DAsystem has a power value of a2 during the state S1 and has a power valueof a3 during the state S0. The power value of a2 is an example of thepower value P21 and the power value of a3 is an example of the powervalue P20.

As indicated in the graph 304, the 60 MHz power signal has the powervalue a2 during states S1 and S0. Moreover, as indicated in graph 306,the 2 MHz signal has a power value of a4 during the state S0. The powervalue a4 is an example of the power value P10. As indicated in graph308, the 60 MHz signal has the power value of a2 when the 2 MHz signalhas the power value of a4.

FIG. 6B shows embodiments of graphs 310, 312, 314, and 316. Each graph310, 312, 314, and 316 plots power values in kilowatts as a function oftime t. As shown in graph 310, instead of the 60 MHz signaltransitioning from the power value of a2 to the power value of a3 (FIG.6A), the 60 MHz signal transitions from the power value of a2 to a powervalue of zero.

Moreover, as shown in graph 312, the 60 MHz signal transitions from thepower value of a2 to a power value of a5, which is an example of thepower value P20. As shown in graph 314, the 60 MHz signal has the powervalue of zero during the state S0 when the 2 MHz signal has a non-zeropower value of a4. As shown in graph 316, the 60 MHz power signal has anon-zero power value of a5 during the state S0 when the 2 MHz signal hasa non-zero power value of a4.

FIG. 7A shows embodiments of graphs 318, 320, 322, and 324. Each graph318, 320, 322, and 324 plots power values in kilowatts as a function oftime t. Graph 318 is similar to graph 302 (FIG. 6A), graph 320 issimilar to graph 304 (FIG. 6A), graph 320 is similar to graph 306 (FIG.6A), and graph 322 is similar to graph 308 (FIG. 6A) except that thegraphs 318, 320, 322, and 324 include a plot of a 27 MHz signal. The 27MHz signal is generated from a 27 MHz DA system (not shown) of the 27MHz generator. The 27 MHz signal is an RF signal having a power value ofa6 during both states S1 and S0.

FIG. 7B shows embodiments of graphs 326, 328, 330, and 332. Each graph326, 328, 330, and 332 plots power values in kilowatts as a function oftime t. Graph 326 is similar to graph 310 (FIG. 6B), graph 328 issimilar to graph 312 (FIG. 6B), graph 330 is similar to graph 314 (FIG.6B), and graph 332 is similar to graph 316 (FIG. 6B) except that thegraphs 326, 328, 330, and 332 include a plot of a 27 MHz signal that hasthe power value of a6.

FIG. 7C shows embodiments of graphs 334, 336, 338, and 340. Each graph334, 336, 338, and 340 plots power values in kilowatts as a function oftime t. Graph 334 is similar to graph 302 (FIG. 6A), graph 336 issimilar to graph 304 (FIG. 6A), graph 338 is similar to graph 306 (FIG.6A), and graph 340 is similar to graph 308 (FIG. 6A) except that thegraphs 334, 336, 338, and 340 include a plot of a 27 MHz signal. The 27MHz signal transitions from having a power value of a7 during the stateS1 to having a power value of a8 during the state S0. The power value a7is less than the power value a8.

FIG. 7D shows embodiments of graphs 342, 344, 346, and 348. Each graph342, 344, 346, and 348 plots power values in kilowatts as a function oftime t. Graph 342 is similar to graph 310 (FIG. 6B), graph 344 issimilar to graph 312 (FIG. 6B), graph 346 is similar to graph 314 (FIG.6B), and graph 348 is similar to graph 316 (FIG. 6B) except that thegraphs 342, 344, 346, and 348 include a plot of a 27 MHz signal that hasthe power values of a7 and a8.

FIG. 7E shows embodiments of graphs 350, 352, 354, and 356. Each graph350, 352, 354, and 356 plots power values in kilowatts as a function oftime t. Graph 350 is similar to graph 302 (FIG. 6A), graph 352 issimilar to graph 304 (FIG. 6A), graph 354 is similar to graph 306 (FIG.6A), and graph 356 is similar to graph 308 (FIG. 6A) except that thegraphs 350, 352, 354, and 356 include a plot of a 27 MHz signal. The 27MHz signal transitions from having a power value of a9 during the stateS1 to having a power value of a10 during the state S0. The power valuea9 is greater than the power value a10.

FIG. 7F shows embodiments of graphs 358, 360, 362, and 364. Each graph358, 360, 362, and 364 plots power values in kilowatts as a function oftime t. Graph 358 is similar to graph 310 (FIG. 6B), graph 360 issimilar to graph 312 (FIG. 6B), graph 362 is similar to graph 314 (FIG.6B), and graph 364 is similar to graph 316 (FIG. 6B) except that thegraphs 358, 360, 362, and 364 include a plot of a 27 MHz signal that hasthe power values of a9 and a10.

It should be noted that in the graphs 302, 304, 306, 308, 310, 312, 314,316, 318, 320, 322, 324, 326, 328, 330, 332, 334, 336, 338, 340, 342,344, 346, 348, 350, 352, 354, 356, and 358 shown above, the 2 MHz signalis shown as a solid line, the 60 MHz signal is shown as a dashed line,and the 27 MHz signal is shown as a dotted line.

FIG. 8 is a block diagram of an embodiment of a system 310 for selectingbetween AFTs 118 and 120 (FIGS. 1 and 3) based on whether a gamma valueis greater than the first threshold or the second threshold. When theTTL signal 112 is in the state S1 and a gamma value measured during thestate S1 exceeds the first threshold, a select logic 128, which is anexample of a selector, of the system 310 selects the AFT 118 and whenthe TTL signal 112 is in the state S0 and a gamma value measured duringthe state S0 exceeds the second threshold, the select logic 128 selectsthe AFT 120. Examples of the select logic 128 include a multiplexer.When the select logic 128 includes the multiplexer, a signal indicatingthat a gamma value measured during the state S1 of the TTL signal 112 isgreater than the first threshold or a signal indicating that a gammavalue measured during the state S0 of the TTL signal 112 is greater thanthe second threshold is received at a select input of the multiplexer.The DSP 150 generates a signal indicating a gamma value measured duringthe state S1 of the TTL signal 112 is greater than the first thresholdand provides the signal to the multiplexer when the TTL signal 112 hasthe state S1. The DSP 150 generates a signal indicating that a gammavalue measured during the state S0 of the TTL signal 112 is greater thanthe second threshold and provides the signal to the multiplexer when theTTL signal 112 has the state S0.

In one embodiment, the select logic 128 includes a processor. In anembodiment, the select logic 128 is implemented within the DSP 140.

When the AFT 118 is selected, the AFT 118 provides the frequency valueF21 to the 60 MHz DA system. Similarly, when the AFT 120 is selected,the AFT 120 provides the frequency value F20 to the 60 MHz DA system.

The 60 MHz DA system generates the 2 MHz signal synchronous with a clocksignal that is received from a clock source 312. In one embodiment, theclock signal of the clock source 312 is asynchronous with the TTL signal112. In an embodiment, the clock signal of the clock source 3112 issynchronous with the TTL signal 112.

In one embodiment, the select logic 128 selects between the powercontrollers 152 and 154 (FIG. 5) instead of the AFTs 118 and 120. Whenthe power controller 152 is selected during the state S1 of the TTLsignal 112, the power controller 152 provides the power value P21 to the60 MHz DA system and when the power controller 154 is selected ruing thestate S0 of the TTL signal 112, the power controller 154 provides thepower value P20 to the 60 MHz DA system.

In one embodiment, the select logic 128 is implemented within the 27 MHzgenerator in a similar manner in which the select logic 128 isimplemented within the 60 MHz generator 276 (FIGS. 1 and 3).

A value of gamma is transferred by the select logic 128 to AFT 118 or120 based on the state S1 or S0. For example, when the state is S1, theDSP 150 provides the first gamma value to the select logic 128. In thisexample, the select logic 128 that has selected the AFT 118 during thestate S1 transfers the first gamma value received from the DSP 150 tothe AFT 118. As another example, when the state is S0, the DSP 150provides the second gamma value to the select logic 128. In thisexample, the select logic 128 that has selected the AFT 120 during thestate S0 transfers the second gamma value received from the DSP 150 tothe AFT 120.

Similarly, in the embodiments in which the power controllers 152 and 154(FIG. 5) are used, the select logic 128 transfers the first gamma valuereceived from the DSP 150 to the power controller 152 during the stateS1 and transfers the second gamma value received from the DSP 150 to thepower controller 154.

Furthermore, in the embodiment in which the select logic 128 isimplemented within the 27 MHz generator and is coupled to powercontrollers of the 27 MHz generator, the select logic 128 transfers athird gamma value received from a DSP of the 27 MHz generator to one ofthe power controllers during the state S1 and transfers a fourth gammavalue received from the DSP to another one of the power controllersduring the state S0. In this embodiment, the third gamma value isgenerated based on the forward and reflected powers on a transmissionline that is coupled to the 27 MHz generator. Also, in this embodiment,both the forward reflected powers are sensed by a sensor of the 27 MHzgenerator. In this embodiment, the fourth gamma value is generated basedon the forward and reflected powers on the transmission line that iscoupled to the 27 MHz generator.

Moreover, in the embodiment in which the select logic 128 is implementedwithin the 27 MHz generator and is coupled to AFTs of the 27 MHzgenerator, the select logic 128 transfers the third gamma value receivedfrom the DSP of the 27 MHz generator to one of the AFTs during the stateS1 and transfers the fourth gamma value received from the DSP to theother one of the AFTs during the state S0.

FIG. 9 is a flowchart of an embodiment of a method 321 for adjusting afrequency and/or power of the 60 MHz DA system to achieve state S1 or S0of the 60 MHz generator 276 (FIGS. 1 and 3). In an operation 325, plasmais struck, e.g., generated, within the plasma chamber 102 (FIG. 1).

In an operation 327, during both states of the TTL signal 112, forwardand reflected powers on the transmission line 232 are measured by thesensor 212 (FIG. 5). The measured forward and reflected powers areconverted from an analog format into a digital format.

In an operation 329, the DSPs 140 and 150 calculate gamma values fromthe digital values of the forward and reflected powers measured duringthe states S0 and S1 of the TTL signal 112. For each state of the TTLsignal 112, a gamma value is determined by a DSP. For example, duringthe state S0 of the TTL signal 112, a gamma value is determined by theDSP 150 based on a relationship between the forward and reflected power,e.g., a square root of a ratio of reflected power to forward powersensed on the transmission line 232, etc., and during the state S1 ofthe TTL signal 112, a gamma value is determined by the DSP 150 based ona relationship between the forward and reflected power, e.g., a squareroot of a ratio of reflected power to forward power sensed on thetransmission line 232 (FIG. 5).

In an operation 331, it is determined whether a gamma value measuredduring the state S1 of the TTL signal 112 is greater than the firstthreshold and it is determined whether a gamma value measured during thestate S0 of the TTL signal 112 is greater than the second threshold. Forexample, the AFT 118 and the power controller 152 determine whether agamma value received from the DSP 150 is greater than the firstthreshold and the AFT 120 and the power controller 154 determine whethera gamma value received from the DSP 150 exceeds the second threshold. Asanother example, the DSP 150 determines whether the first gamma value isgreater than the first threshold or the second gamma value is greaterthan the second threshold.

Upon determining that the gamma value is greater than the firstthreshold, in an operation 333, the AFT 118 provides the frequency valueF21 to the 60 MHz DA system and the power controller 152 provides thepower value P21 to the 60 MHz DA system. Moreover, upon determining thatthe gamma value is greater than the second threshold, in an operation335, the AFT 120 provides the frequency value F20 to the 60 MHz DAsystem and the power controller 154 provides the power value P20 to the60 MHz DA system. The operation 327 of the method 321 repeats after theoperations 333 and 335.

Although the method 321 is described with respect to the 60 MHzgenerator 276, in one embodiment, the method 321 applies to the 27 MHzgenerator or a generator with a frequency other than 27 MHz or 60 MHz.

FIG. 10 shows an embodiment of a graph 400 of normalized RF variablesversus time for implementing RF tuning by the dependent RF generator foroptimal production time power delivery during IP RF signal pulsing.Examples of the normalized RF variables include forward power and gammavalues. FIG. 10 may be better understood when studied in conjunctionwith a flowchart of a method 500, an embodiment of which is shown inFIG. 11. The method 500 provides details regarding operations forimplementing frequency tuning by the dependent RF generator for optimalpower delivery during pulsing.

At a point 402, the 2 MHz IP RF generator is pulsed high and the 60 MHzdependent RF generator is set to its previously learned optimal RFfrequency of IDPC_Freq1 (e.g., 61.3 MHz) or allowed to self-tune to thisoptimal RF frequency of IDPC_Freq1. This is seen in an operation 504 ofFIG. 11. Thereafter, the dependent RF generator operates in thefrequency tuning mode.

In the example of FIG. 10, the 2 MIIz IP RF signal pulses at a pulsingfrequency of 159.25 Hz with a 50% duty cycle, which may vary if desired,between a high power set point of 6 kW and a low power set point of 0kW, which is not a requirement and can be non-zero. The 60 MHz dependentRF generator provides power at a power set point of 900 W. While the 60MHz dependent RF generator delivers power to the plasma load within theplasma chamber 102, the dependent RF generator also monitors the gammavalue via the sensor 212 as illustrated in operations 506 and 508 ofFIG. 11.

At a point 404, the 2 MHz IP RF signal pulses low to a point 409.Shortly after this high-to-low transition, a gamma value measured by the60 MHz dependent RF generator spikes from around 0.04 to around 0.8,e.g, from a point 407 to a point 408. If the IDPC_Gamma1 threshold isset at, e.g., 0.7, an excursion by the detected gamma value (branch YESof the operation 508) facilitates the 60 MHz RF generator to flip fromone previously learned optimal tuned RF frequency value of IDPC_Freq1 tothe other previously learned optimal tuned RF frequency value ofIDPC_Freq2. This is seen in an operation 510 of FIG. 11. This tuning ofthe 60 MHz dependent RF generator from IDPC_Freq1 to IDPC_Freq2 inresponse to the high-to-low transition of the 2 MHz IP RF signalachieves a measured gamma value down to 0.05, e.g., from the point 410to a point 412.

At a point 415, the 2 MHz IP RF signal pulses from low to high, e.g.,reaches a point 417. Shortly after this low-to-high transition, a gammavalue is measured in operations 512 and 514 by the dependent RFgenerator spikes from around 0.05 to around 0.78. The spike isillustrated between points 414 and 416.

If the IDPC_Gamma2 threshold is set at to trip at, for example, 0.75,the excursion by the detected gamma value, e.g., a YES branch of anoperation 514 of FIG. 11, facilitates the 60 MHz RF generator to flipfrom the previously learned optimal tuned RF frequency value IDPC_Freq2to the other previously learned optimal tuned RF frequency value ofIDPC_Freq1. This is seen in the operation 504 of FIG. 11. This tuning ofthe 60 MHz dependent RF generator from IDPC_Freq2 to IDPC_Freq1 inresponse to the low-to-high transition of the 2 MHz IP RF signal bringsthe measured gamma value down to 0.04, e.g., from the point 418 to apoint 420.

It should be noted that the time scale of FIG. 10 reflects a faster timescale than that of FIG. 3. The time scale of FIG. 10 illustratesproduction time and the time scale of FIG. 3 illustrates learning time.This is the case when, as mentioned, the high duration and the lowduration of the IP RF pulse are artificially extended during learningtime to permit the dependent RF generator to self-tune to the optimaltune RF frequencies for learning purposes. It should further be notedthat the 60 MHz signal is illustrated as a signal 460 in FIG. 10.

In one embodiment, during production time, such self-tuning is not usedsince the dependent RF generator operates essentially as a state machineand flips from one learned optimal RF frequency to another learnedoptimal RF frequency as it detects the high-to-low transition of the IPRF signal and the low-to-high transition of the IP RF signal. Thehigh-to-low transition is detected by comparing a measured gamma valueto the IDPC_Gamma1 threshold and by determining the previous state ofthe IP RF signal prior to the detection of the gamma excursion.Moreover, the low-to-high transition is detected by comparing themeasured gamma value versus the IDPC_Gamma2 threshold and by determiningthe previous state of the IP RF signal prior to the detection of thegamma excursion.

It should be noted that although the above-described embodiments relateto providing the 2 MHz RF signal and/or 60 MHz signal and/or 27 MHzsignal to the lower electrode 104 and grounding the upper electrode 110,in several embodiments, the 2 MHz, 60 MHz, and 27 MHz signals areprovided to the upper electrode 110 while the lower electrode 104 isgrounded.

It is also noted that in one embodiment, an input, e.g., frequencyinput, power input, etc., or a level, e.g., power level, frequencylevel, includes one or more values that are within a limit, e.g.,standard deviation, etc., of another value. For example, a power levelincludes the power value P21 and other power values that are within thelimit of the power value P21. In this example, the power level excludesany power values for another state, e.g., power value P20 for state S0.As another example, a frequency input includes the frequency value F11and other frequency values that are within a limit of the frequencyvalue F11. In this example, the frequency input excludes any frequencyvalues for another state, e.g., frequency value F10 for state S0.

It is noted that although the above-described embodiments are describedwith reference to parallel plate plasma chamber, in one embodiment, theabove-described embodiments apply to other types of plasma chambers,e.g., a plasma chamber including an inductively coupled plasma (ICP)reactor, a plasma chamber including an electron-cyclotron resonance(ECR) reactor, etc. For example, the 2 MHz and the 60 MHz power suppliesare coupled to an inductor within the ICP plasma chamber.

Moreover, although some of the above embodiments are described usinggamma values, in an embodiment, impedance difference values can be used.For example, when the state of the TTL signal 112 is S1, the DSP 150determines an impedance from reflected power over the transmission line232 and also determines an impedance from forward power over thetransmission line 232. The DSP 150 determines whether a first differencebetween the impedances exceeds a first limit and upon determining so,sends a signal indicating so and also indicating a value of the firstdifference. Upon receiving the signal indicating the value of the firstdifference, the AFT 118 retrieves from a memory device the frequencyvalue F21 and the power controller 152 retrieves from a memory devicethe power value P21. The values F21 and P21 are then provided to the 60MHz DA system.

Similarly, when the state of the TTL signal 112 is S0, the DSP 150determines an impedance from reflected power over the transmission line232 and also determines an impedance from forward power over thetransmission line 232. The DSP 150 determines whether a seconddifference between the impedances exceeds a second limit and upondetermining so, sends a signal indicating so and also indicating a valueof the second difference. Upon receiving the signal indicating the valueof the second difference, the AFT 120 retrieves from a memory device thefrequency value F20 and the power controller 154 retrieves from a memorydevice the power value P20. The values F20 and P20 are then provided tothe 60 MHz DA system.

In one embodiment, the operations performed by an AFT and/or a powercontroller of a generator controller are performed by a DSP of thegenerator controller. For example, the operations, described herein, asperformed by the AFT 118 and 120 are performed by the DSP 150.

In an embodiment, the terms “driver and amplifier” and “DA system” areused interchangeably herein.

Embodiments described herein may be practiced with various computersystem configurations including hand-held devices, microprocessorsystems, microprocessor-based or programmable consumer electronics,minicomputers, mainframe computers and the like. The embodiments canalso be practiced in distributed computing environments where tasks areperformed by remote processing devices that are linked through anetwork.

With the above embodiments in mind, it should be understood that theembodiments can employ various computer-implemented operations involvingdata stored in computer systems. These operations are those requiringphysical manipulation of physical quantities. Any of the operationsdescribed herein that form part of the embodiments are useful machineoperations. The embodiments also relates to a device or an apparatus forperforming these operations. The apparatus may be specially constructedfor a special purpose computer. When defined as a special purposecomputer, the computer can also perform other processing, programexecution or routines that are not part of the special purpose, whilestill being capable of operating for the special purpose. Alternatively,the operations may be processed by a general purpose computerselectively activated or configured by one or more computer programsstored in the computer memory, cache, or obtained over a network. Whendata is obtained over a network the data may be processed by othercomputers on the network, e.g., a cloud of computing resources.

One or more embodiments can also be fabricated as computer-readable codeon a non-transitory computer-readable medium. The non-transitorycomputer-readable medium is any data storage device that can store data,which can be thereafter be read by a computer system. Examples of thenon-transitory computer-readable medium include hard drives, networkattached storage (NAS), ROM, RAM, compact disc-ROMs (CD-ROMs),CD-recordables (CD-Rs), CD-rewritables (CD-RWs), magnetic tapes andother optical and non-optical data storage devices. The non-transitorycomputer-readable medium can include computer-readable tangible mediumdistributed over a network-coupled computer system so that thecomputer-readable code is stored and executed in a distributed fashion.

Although the method operations in the flowcharts above were described ina specific order, it should be understood that other housekeepingoperations may be performed in between operations, or operations may beadjusted so that they occur at slightly different times, or may bedistributed in a system which allows the occurrence of the processingoperations at various intervals associated with the processing, as longas the processing of the overlay operations are performed in the desiredway.

One or more features from any embodiment may be combined with one ormore features of any other embodiment without departing from the scopedescribed in various embodiments described in the present disclosure.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications can be practiced within the scope ofthe appended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein, but may be modifiedwithin the scope and equivalents of the appended claims.

1. A system comprising: a plasma chamber for containing plasma, theplasma chamber including an electrode; a driver and amplifier coupled tothe plasma chamber for providing a radio frequency (RF) signal to theelectrode, the driver and amplifier coupled to the plasma chamber via atransmission line; a selector coupled to the driver and amplifier; afirst auto frequency control (AFC) coupled to the selector; a second AFCcoupled to the selector, wherein the selector is configured to selectthe first AFC or the second AFC based on values of current and voltagesensed on the transmission line.
 2. The system of claim 1, wherein thevalues of current and voltage are used to generate one or more values ofgamma, wherein the selector is configured to select the first AFC whenone of the values of gamma is greater than a first threshold and isconfigured to select the second AFC when another one of the values ofgamma is greater than a second threshold.
 3. The system of claim 1,wherein the selector includes a multiplexer.
 4. A system comprising: aprimary generator coupled to an electrode, the primary generatorincluding a primary driver and amplifier for supplying a primary radiofrequency (RF) signal to the electrode, the primary generator furtherincluding a primary automatic frequency tuner (AFT) to provide a firstprimary frequency input to the primary driver and amplifier when apulsed signal is in a first state, the primary AFT configured to providea second primary frequency input to the primary driver and amplifierwhen the pulsed signal is in a second state; and a secondary generatorcoupled to the electrode, the secondary generator including a secondarydriver and amplifier for supplying a secondary RF signal to theelectrode, the secondary generator further including a first secondaryAFT coupled to the secondary driver and amplifier, the secondarygenerator including a second secondary AFT coupled to the secondarydriver and amplifier, the secondary generator including a processor, theprocessor coupled to the first secondary AFT and the second secondaryAFT, the secondary generator further including one or more sensorscoupled to the electrode, the one or more sensors for sensing currentand voltage transferred between the secondary generator and theelectrode during the first and second states, the processor configuredto generate parameters based on the current and voltage, the processorconfigured to determine whether a first one of the parameters for thefirst state exceeds a first boundary and whether a second one of theparameters for the second state exceeds a second boundary, the firstsecondary AFT configured to provide a first secondary frequency input tothe secondary driver and amplifier upon receiving the determination thatthe first parameter exceeds the first boundary, the second secondary AFTconfigured to provide a second secondary frequency input to thesecondary driver and amplifier upon receiving the determination that thesecond parameter exceeds the second boundary.
 5. The system of claim 4,further comprising a selector coupled to the processor for selecting thefirst secondary AFT or the second secondary AFT, the selector forselecting the first secondary AFT in response to receiving a signal fromthe secondary processor indicating that the first parameter exceeds thefirst boundary, the selector for selecting the second secondary AFT inresponse to receiving a signal from the secondary processor indicatingthat the second parameter exceeds the second boundary.
 6. The system ofclaim 4, wherein the electrode includes a lower electrode of a plasmachamber.
 7. The system of claim 4, wherein during the first state, theprimary driver and amplifier is configured to generate the primary RFsignal having a lower frequency than that of the secondary RF signal,wherein the primary RF signal has a higher amount of power than thesecondary RF signal.
 8. The system of claim 4, wherein the processor isconfigured to determine whether the pulsed signal is in the first or thesecond state based on a magnitude of the pulsed signal.
 9. The system ofclaim 4, wherein each of the first and second parameter includes a gammavalue or an impedance difference value.
 10. A system comprising: adigital pulsing source for generating a pulsed signal; a primarygenerator including: a primary driver and amplifier coupled to anelectrode for supplying a primary radio frequency (RF) signal to theelectrode; one or more primary processors coupled to the pulsing sourcefor receiving the pulsed signal, the one or more primary processorsconfigured to: identify a first one of two states of the pulsed signaland a second one of the two states; determine to provide a primary powervalue to the primary driver and amplifier when the pulsed signal is inthe first state; and determine to provide a primary frequency value ofthe primary RF signal when the pulsed signal is in the first state; anda secondary generator including: a secondary driver and amplifiercoupled to the electrode for supplying a secondary RF signal to theelectrode; one or more secondary processors coupled to the pulsingsource for receiving the pulsed signal, the one or more secondaryprocessors configured to: determine whether a parameter associated withplasma exceeds a first boundary when the pulsed signal is in the firststate; determine whether the parameter exceeds a second boundary whenthe pulsed signal is in the second state; determine to provide a firstsecondary power value to the secondary driver and amplifier in responseto determining that the parameter exceeds the first boundary; determineto provide a second secondary power value to the secondary driver andamplifier in response to determining that the parameter exceeds thesecond boundary; determine to provide a first secondary frequency valueto the secondary driver and amplifier in response to determining thatthe parameter exceeds the first boundary; and determine to provide asecond secondary frequency value to the secondary driver and amplifierin response to determining that the parameter exceeds the secondboundary.
 11. The system of claim 10, further comprising a selectorcoupled to the one or more secondary processors for selecting the firstsecondary frequency value or the second secondary frequency value, theselector for selecting the first secondary frequency value in responseto receiving a signal from the one or more secondary processorsindicating that the first parameter exceeds the first boundary, theselector for selecting the second secondary frequency value in responseto receiving a signal from the one or more secondary processorsindicating that the second parameter exceeds the second boundary. 12.The system of claim 10, wherein the parameter includes a gamma value oran impedance difference value.
 13. The system of claim 10, wherein theelectrode includes a lower electrode of a plasma chamber.
 14. The systemof claim 10, wherein during the first state, the primary driver andamplifier is configured to generate the primary RF signal having a lowerfrequency than that of the secondary RF signal, wherein the primary RFsignal has a higher amount of power than the secondary RF signal. 15.The system of claim 10, wherein each of the primary and secondaryfrequency values are tuned.
 16. The system of claim 10, wherein the oneor more primary processors determine whether the pulsed signal is in thefirst or the second state based on a magnitude of the pulsed signal. 17.A method comprising: receiving a digital pulsing signal, the digitalpulsing signal having two states; receiving current and voltage values;calculating parameters associated with plasma impedance from the currentand voltage values; determining during the first state whether a firstone of the parameters exceeds a first boundary; providing a firstfrequency value and a first power value to a radio frequency (RF) driverand amplifier upon determining that the first parameter exceeds thefirst boundary; determining during the second state whether a second oneof the parameters exceeds a second boundary; and providing a secondfrequency value and a second power value to the RF driver and amplifierupon determining that the second parameter exceeds the second boundary.18. The method of claim 17, wherein the method is used to processsemiconductor wafers to make integrated circuits.
 19. The method ofclaim 17, wherein the parameters include gamma values or impedancedifference values.
 20. The method of claim 17, further comprisingselecting between providing the first frequency value and the firstpower value or the second frequency value and the second power value.